The present invention relates to apparatus for cleaning electrostatically adhered particles from moving sheets and webs.
In many industries, sheets and webs of indeterminate length are fed to various processing apparatus, said such as printing, gluing, winding, etc. It is important in many instances that these sheets and webs be cleaned, and it has therefore been proposed to blow air on them to remove dust and other particles.
A known sheet and web cleaning apparatus is disclosed in Testone U.S. Pat. No. 4,454,621, having a pair of spaced, opposed suction hoods, between which there is transported a sheet or web to be cleaned. The suction hoods are made of formed sheet metal, and are of increasing cross-sectional area from a first end, towards a second end to which a suction hose or the like is connected. The suction hood is provided with an inlet slot which is of tapering width, being wider remote from the second end where the suction hose is connected. Adjacent the surface of the suction hood containing the inlet slot, there is a housing which contains a pair of pressurized ionizing bars in spaced, parallel relationship, providing between them a suction slot which enables air to be drawn through it and into the suction hood. A throat plate is attached to each housing, and the sheet or web passes between the throat plates. In this construction, air flowing through the inlet slot of the suction hood is comprised of air discharged by the pressurized ionizing bars, and by additional air drawn from atmosphere and passing between the throat plate and the moving sheet or web. The speed of the sheet or web was substantially less than 3,000 feet per minute.
The above described prior art apparatus was found to have a number of deficiencies. In order to remove as many particles as possible, a relatively high flow of air including ions, was required to be drawn into the suction hood. However, in some instances, the low pressure created by this flow of air was found to cause some sheets or webs to adhere to one or the other of the throat plates, thus substantially inhibiting air flow into the suction hood. The result was that a portion of the sheet or web was not cleaned, and in some instances the sheet or web was drawn into the suction slot. This required that the entire sheet or web feeding and handling apparatus be stopped, and the blowers of the sheet and web cleaner cut off, so that the attraction of the sheet or web to the sheet and web cleaner could be broken. This was time consuming, required labor to remedy the situation, and caused interruption of production.
Another problem with the above noted sheet and web cleaner is that the metal throat plates became scratched through use. The throat plates were the parts of the sheet and web cleaner closest to the sheet or web being fed. As some of these sheets or webs were prone to scratching and since such scratching was unacceptable, there occurred this further deficiency in the noted prior art apparatus. In particular, if the sheet or web was coated paper or plastic film such those of acetate and Mylar, they were readily harmed by scratches.
Further, the sheet and web cleaner did not clean the sheet and web to the extent desired, because it has been found that in some instances it dislodged a particle from the sheet or web, which was not removed by suction, but adhered to the apparatus, and then became attached to the sheet or web, after the sheet or web had been subjected to the cleaning action.
The above described sheet and web cleaner was also expensive to manufacture. It required substantial effort to form a number of sheet metal parts, and to assemble the many parts including suction hoods, ionizing bars, housings for the ionizing bars, and throat plates.